This invention relates generally to disc-type roller cutters used for cutting hard rock, and more particularly, to disc-type cutters of the single disc type of small or compact size which are adapted for use on small diameter hard rock tunnelling machines, such as those used for tunnels having a diameter in the range of 0.5 to 2 meters.
Tunnel boring machines, particularly for those used in hard rock formations, bore a cylindrical tunnel using a single cutter head which rotates about the axis of the tunnel and is pushed forward against the rock face by suitable hydraulic thrust cylinders which react against a frame that grips the side walls of the tunnel already cut, or, in the case of small diameter machines, react against the installed tunnel lining.
The cutter head is provided with a number of cutters on its face, the number of which generally depends upon the diameter of the tunnel being cut, and these cutters are generally positioned at various places around the face of the cutter head in a pattern which provides balance loading around the axis for uniform thrust purposes and proper spacing to provide the desired uniform cutting over the working face of the tunnel. While stationary pick-type cutters may be used in soft ground, it has been found that in cutting rock, a disc-type cutter which rolls about an axis parallel to the tunnel face is far more efficient and has far longer life. If the rock is not too hard, a cutter may have a number of circular edges projecting from a single member which rotates about a shaft whose ends are mounted on a suitable saddle attached to the cutter head. However, when harder rock is encountered, each cutter generally has a single edge mounted on a short shaft which allows greater thrust forces per cutting edge to be used for the cutter head.
Heretofore, the trend has been to use larger and larger diameter cutters because these allow greater thrust forces and because the larger sized cutters can employ higher capacity bearings while providing adequate bearing life in use. However, past cutter design has required cutters of such a size that they can generally only be used on tunnels that are two meters in diameter or larger, since proper cutting action requires such a multiplicity of cutters that there is not adequate space for larger cutters on a smaller sized cutter head.
For this reason, smaller diameter cutter heads, generally those of less than two meters in diameter, have used cutters which are mounted on a cantilever shaft extending from a pedestal-type mount. These cutters were often of the multi-row-type having a plurality of cutter rings formed on a single member, or with a large number of hard carbide buttons in the place of the annular rings. With such cutters, the cantilever construction results in limitations on the total thrust force of the cutter head against the rock. Thus, to provide improved cutting action, greater numbers of cutters are required, with the force of each cutting edge against the rock being much lower than desired. The result is a slower cutting action with increased energy requirements because the rock tends to be broken into smaller and smaller pieces.